The purpose of the present invention is to increase the combustion efficiency of an oil burner, especially those of the gun-type employing a liquid fuel atomizing nozzle discharging a hollow or solid conical fuel spray. Such oil burners are commonly used in home furnaces and boilers as well as in many commercial furnaces and boilers. In such conventional oil burners, the air is introduced through a blast tube in the vicinity of the oil emanating from the nozzle so as to intermingle with the oil. The mixture is ignited typically by a pair of high voltage electrodes.
In order to obtain nearly complete combustion of the emanating oil it has been necessary to use more than the amount of air which would theoretically be necessary to oxidize (burn) the fuel oil. As is well known in the art, the No. 2 fuel oil commonly used in such oil burners consists primarily of molecular combinations of carbon and hydrogen. Each of these elemental components burn independently and separately combine with a part of the oxygen present in the emanating air. According to a publication entitled "Technician's Manual", Education Publication ED 70 211, page F.O.D.B.-20, the hydrogen component of the oil, being a highly combustible gas, oxidizes faster and requires a smaller amount of air as compared to the carbon component of the oil in order to oxidize. The hydrogen oxidizes in the ratio of two parts of hydrogen to one part of oxygen to form water vapor. If there was no more air available, the remaining carbon in the fuel oil would be thrown off to become a carbon deposit, commonly called soot. However, if additional air is admitted through the blast tube, one part carbon will combine with one part oxygen to yield carbon monoxide (CO), which is also a combustible gas. If more air is available, there will likewise be more oxygen available so that one part carbon will combine with two parts of oxygen to form carbon dioxide (CO.sub.2), which is a non-combustible gas representing complete combustion of the fuel oil.
The No. 2 fuel oil commonly used in home furnaces and boilers contains approximately 140,000 British thermal units (BTU's) per gallon (9,340,000 calories per liter). If complete combustion of the oil were obtained with no excess oxygen, the products of combustion would be water vapor (oxidation of the hydrogen), carbon dioxide (oxidation of the carbon), and nitrogen (the primary remaining constituent of air which does not take part in the combustion of the fuel oil). For the No. 2 fuel oil utilized in conventional oil burners, the highest theoretical percentage of carbon dioxide in these products of combustion is 15.6%. This represents a chemical reaction where all the hydrogen and carbon in the fuel oil is completely oxidized with no excess air. Such a chemical reaction is called a stoichiometric reaction. In most conventional oil burners, a percentage of between 10 and 12% carbon dioxide in the combustion products is the highest obtainable percentage due to the necessity of utilizing excess oxygen and therefore excess air to obtain complete combustion of fuel oil. The percentage of excess air as a function of the carbon dioxide percentage is given below (values obtained from above mentioned "Technician's Manual", page O.B.T.C.T.-48):
______________________________________ % CO.sub.2 % Excess Air ______________________________________ 15.5 0 14 7 12 25 10 50 8 81 6 142 4 218 ______________________________________
The present invention through experimental testing has been able to obtain better than 15% carbon dioxide in the combustion products (less than 7% excess air), while maintaining nearly complete combustion of the oil with no carbon buildup (soot) on the diffuser or parts of the conventional oil burner. This represents a reduction of excess air or more than 18 to 43 percent as compared to conventional oil burners.
Thus, in general, a device for improving the combustion efficiency of an oil burner must attempt to minimize the amount of excess air needed for as complete as possible combustion of the fuel oil. It must also minimize the buildup of smoke within the combustion chamber and carbon deposits on the combustion improving device and other parts of the oil burner. Otherwise the carbon buildup can impair or even stop the operation of the oil burner (especially the oil nozzle and igniting electrodes) and can dramatically reduce the heat conducting transfer efficiency of the oil burner heat exchanger.
In actual operation, the amount of smoke present in the combustion product is measured by the Bacharach True Spot Smoke Tester, a device which is well-known in the oil heating art. The combustion efficiency is usually measured by measuring the amount of carbon dioxide in the exhaust gases since carbon dioxide is the easiest product of combustion to quantitatively measure. Its measurement is usually made with a fyrite carbon dioxide analyzer, another device well-known in the oil heating art.
Although a number of prior art devices have been disclosed which attempt to increase combustion efficiency, none of these devices disclose or suggest an oil burner combustion efficiency improving device mounted at the end of a gun-type burner blast tube having a forwardly or downstream positioned cone with an upstream central opening, a plurality of holes circularly spaced about the central opening in a configuration which, when taken in conjunction with a rearwardly extending cylindrical member mounted to the outer periphery of the cone and a back ring radially extending inwardly from the rearward termination of the cylindrical member, provides for nearly complete combustion of the fuel oil with a minimum of excess air and wihout carbon buildup on the diffuser itself or on components of the gun-type burner. Although all of the reasons why the present invention is able to achieve nearly complete combustion of the fuel oil with minimum excess air and without carbon buildup are not completely understood, it is believed that the attributes of the present invention are at least in part due to obtaining a rotationally static air flow pattern emanating from the diffuser cone such that the intermixing of the air with the fuel oil approaches an ideal state. The air flow pattern also prevents the oil droplets, which typically exit from the oil nozzle in a hollow cone pattern, from at least contacting the inner half of the cone front surface. Although it has not been empirically established, it may also be that the present diffuser actually prevents oil droplet deposition throughout the cone front surface. In any event, the outer portion of the cone where oil may come in contact is sufficiently hot to self clean any carbon deposits. Thus, no carbon buildup is obtained and therefore fouling of the diffuser and oil burner parts is prevented.
The following prior art references are believed to be relevant with respect to the present invention:
______________________________________ U.S. Pat. No. Inventor Date of Issue ______________________________________ 1,953,483 Higinbotham 1934 2,090,566 Andler 1937 2,090,567 Andler 1937 2,109,027 McCullough 1938 2,502,664 Nest 1950 2,665,748 Cornelius 1954 2,790,490 Smith 1957 3,003,548 Sanders et al 1961 3,211,207 Luft 1965 3,360,929 Drewry 1968 3,404,844 Walsh 1968 3,406,002 Martin 1968 3,409,231 Oehlerking 1968 3,490,858 Fletcher 1970 3,493,180 Walsh 1970 3,529,917 Hindenlang 1970 3,574,508 Rothhaar 1971 3,632,286 Kegan et al 1972 3,694,135 Dancy et al 1972 3,733,169 Lefebvre 1973 3,869,242 Creuz 1975 3,881,863 Creuz 1975 3,923,251 Flournoy 1975 4,012,189 Vogt et al 1977 West German Patent 386,159 1923 ______________________________________
Copies of these references will be made part of the patent application file.
More particularly, U.S. Pat. No. 1,953,483, Higinbotham, discloses an oil burner having a head with a curved passage for discharge of air in a whirling motion and a deflector to direct air across the face of an oil burner nozzle, the head having an orifice for the passage therethrough to air to provide an air cushion for the head and the whirling air providing a counter current which, together with the air cushion, impinges upon the oil spray. The air pattern arrangement of this oil burner is highly different than that obtained by the present invention. It also does not disclose or suggest the hole pattern and diffuser cone shape for obtaining the air pattern of the present invention.
U.S. Pat. Nos. 2,090,566 and 2,090,567, Andler, both basically disclose the same invention, including a deflection disc 6 for generating an air flow in the shape of an annulus having a gyrating motion when it is discharged through a space generated by an inwardly tapering wall 9 and a truncated cone 10 with the result that it is formed into a vortex. It is disclosed that the oil is sprayed from an end 11 of the blast tube into this gyrating lamina of air so that it is mixed for combustion. Neither of these references disclose the shape, hole pattern, and resulting air pattern obtained by the present invention.
U.S. Pat. No. 2,109,027, McCullough, discloses a mixing well or ball adjacent the nozzle of an oil burner for mixing the air before it passes over the nozzle in order to obtain more thorough mixing and more efficient burning. The end of the nozzle has an inner surface 9 directing air inward toward the center of the tube to a theoretical point 10. Such an air flow direction is highly different from the rotationally static air flow obtained by the present invention. This reference also does not disclose the hole pattern, cone shape and back ring arrangement as disclosed in the present invention.
Likewise, the multiplicity of slit openings disclosed in U.S. Pat. No. 2,502,664, Nest, preferably spaced in the form of louvers 12 so as to separate the main air stream into a multiplicity of overlapping streams of air issuing into a form that resembles ribbons to produce a stable vortex at the point of flame propogation is again different than the rotationally static shaped fuel/air mixing obtained by the present oil diffuser.
Although U.S. Pat. No. 2,665,748, Cornelius, discloses air passages 49 and 51, the arrangement of these air passages is unlike the hole pattern of the present invention. The Cornelius reference discloses the generation of a rotary stream of air about the burning stream of sprayed liquid fuel while the fuel is being converted into a gaseous form so as to reduce noise and to prevent deposition of carbon on the inner surface of combustion head 22. Although the present invention obtains carbon free combustion, it is believed to be in part due to the air stream pattern and also due to the elevated operating temperature of the diffuser rather than a rotary air pattern as disclosed by Cornelius.
U.S. Pat. Nos. 2,790,490, Smith; 3,003,548, Sanders et al, 3,211,207, Luft; 3,404,844, Walsh; 3,406,002, Martin; 3,409,231, Oehlerking; 3,390,858, Fletcher; and 3,493,180, Walsh, all disclose various oil burners and oil burner attachments which also generate either a whirling air motion by use of vanes and the like or a diverging air flow pattern by use of hollow cones such as that disclosed in Sanders et al. None of these references disclose or suggest the use of an oil burner diffuser having a cone shape and an air hole pattern as well as a back ring for effecting a rotationally static air flow pattern in the vicinity of the emanating oil spary. Likewse, U.S. Pat. No. 3,574,508, Rothhaar et al, although disclosing a burner assembly having a cone 34 incorporating a plurality of holes with the fuel nozzle 50 positioned at the narrowmost end of the cone, its resulting air pattern obtained as the air is forced over the outer portion of the cone is of a swirling motion so as to mix with the gas fuel emanating from the nozzle 50. Disclosure of such a hole pattern is unlike that of the present invention and clearly obtains an air flow pattern unlike that of the present invention.
This result is similarly true with respect to German Pat. No. 386,159 which discloses a dam nozzle-ring 4 placed in front of an air-nozzle 6, the nozzle-ring having nozzles 4.sup.a or 4.sup.b as shown in FIG. 2 thereof. These nozzles or vanes have a smaller cross-section at their air entering side than at their air exiting side so that air passing through them is directed either radially inward or tangentially to the emanating oil from the burner nozzle 5 (see FIG. 1 thereof). Thus, the primary object of the German patent is to control the amont of air that flows through nozzle-ring 4 and fire-ring 3 by means of a ring-bolt 2 having slits 7. This ring-bolt can be moved laterally with respect to the fire-head so as to allow more or less air to pass therethrough and thereby allow more or less air to pass through vanes 4.sup.a or 4.sup.b of nozzle-ring 4. The hole pattern shown in this reference is unlike the hole pattern of the present oil diffuser and the method of entering air through the vanes is completely unlike that of the present oil diffuser.
Other references which disclose for use with oil burners which create swirling air motions and which do not utilize the conically shaped diffuser with a hole pattern are U.S. Pat. Nos. 3,694,135, Dancy et al; 3,733,169, Lefebvre; and 3,923,251, Flournoy.
The remaining references are directed to fuel burners and attempts to improve their combustion efficiency and turn down ratio. Thus, U.S. Pat. No. 3,360,929, Drewry, discloses a gas turbine combustor utilizing a conical casing within a tube for receiving a flow of compressed air. The casing has an apex with an opening of a size to accommodate a nozzle of a type able to discharge a hollow conical spray within the conical casing. The device also has a guiding cone supported concentrically within the conical casing to form a mixing space therebetween for receiving the hollow spray, the air apertures spaced around the conical casing which cause air to be jetted at high velocity into the mixing space to provide for violent intermixing of air and oil at an early stage before the mixture passes beyond the guiding cone. A review of the figures contained in this reference discloses that the air is not rotationally static but appears to take on a rotary or swirling type motion. This reference also does not disclose or suggest the air hole pattern of the present oil burner diffuser nor the back ring associated as an integral part of this diffuser.
U.S. Pat. No. 3,632,286, Kegan et al, discloses a grid burner suitable for combustion of either a gas or liquid fuel including gutter-type flame holders 10. This reference does not disclose the use of holes in a conical diffuser or the use of a back ring association with such a diffuser.
U.S. Pat. No. 3,529,917, Hindenlang, discloses an air-mixing device for fuel burners having three different embodiments as shown in FIGS. 3-6. All of these embodiments cause the emanating air in the vicinity of the nozzle to converge radially inwardly to a certain extent, at least in the radial vicinity of the oil burner nozzle. The shape of member 60 including the passage hole 64 therein is unlike the air hole pattern of the present invention.
U.S. Pat. Nos. 3,869,243 and 3,881,863, both Creuz, are directed to improvements in gas/oil burners to substantially increase the turn-down ratio or to be used with very high turn-down ratio burners. The turn-down ratio is the ratio between the maximum fuel infeed rate and the minimum fuel infeed rate for which satisfactory operation of the burner can be obtained. In the '243 reference, the improved air damper structure and linkage of the damper to a fuel ratio control opens the damper only at moderate fuel infeed rates. Although a cone 11 is disclosed having holes 21, its hole pattern is substantially different than that of the present oil burner diffuser. Furthermore, the apparent air flow pattern of the '243 reference is unlike the rotationally static air flow obtained by the present invention since the air entering the environs of cone 11 does not do so from a blast tube as does the present invention.
The '863 reference discloses a burner cone 15 having a number of air apertures 16 in a number of circular rows increasing in size from the small upstream end to the large downstream end. Such a hole pattern is unlike that of the present oil burner diffuser. Furthermore, although the last row of apertures at the large end of the disclosed burner cone are used to provide a cylindrically shaped air curtain extending downstream from the burner, similar to the purpose for the outermost row of holes in the present oil burner diffuser, the other aspects of the present invention including the particular air hole pattern within the cone, the angular opening of the cone, and the back ring of the cone are neither disclosed nor suggested by the '863 reference.
Finally, U.S. Pat. No. 4,012,189, Vogt et al, is directed to a hot gas generator for production of hot combustion gases and includes a cylindrical combustion chamber having an inner and outer conduit concentrically disposed thereabout. This reference does not disclose or suggest the air hole pattern of the present oil burner diffuser so as to generate a rotationally static fuel/air mixing zone.
For all of the reasons presented above, it is believed that the present oil burner diffuser is neither disclosed nor suggested by any of these references taken alone or in logical combination with each other.